1. Field of the Invention
The present invention relates to a power supply apparatus, and more particularly, to a power supply apparatus having a multi-output supplying power to a light emitting diode.
2. Description of the Related Art
Recently, in the area of displays, a display apparatus using a cathode ray tube (CRT) has been replaced with a flat panel display (FPD) reflecting user demands for features such as a high resolution, large screens, and the like.
Particularly, in the case of a large display apparatus, a liquid crystal display (LCD) has rapidly grown due to an advantage thereof in view of lightness and slimness and such an LED is expected to play a leading role in view of cost and marketability.
Meanwhile, in an existing liquid crystal display apparatus, a cold cathode fluorescent lamp (CCFL) has mainly been used as a backlight light source. However, recently, a light emitting diode (LED) has been gradually used as the backlight light source due to various advantages such as low power consumption, a long lifespan, environmentally-friendly features, and the like.
In order to drive a light emitting diode, a power supplying circuit converting commercial alternating current (AC) power into direct current (DC) power and a driving circuit controlling the supplying of the DC power to the light emitting diode are generally used.
The power supplying circuit may be divided into a primary side and a secondary side based on a transformer, in order to enhance an insulation function, wherein the primary side is configured of a circuit rectifying and smoothing the commercial AC power to switch the power and the secondary side is configured of a circuit rectifying power of which a voltage is transformed by the transformer and supplying the rectified power to a load.
That is, as disclosed in the following Related Art Document, generally, a power switching control circuit is formed on the primary side and the above-mentioned driving circuit is formed on the secondary side. In this configuration, in order to smoothly control switching of the power, information regarding a state of the power supplied to the light emitting diode should be fed back and the switching of the power should be controlled based on the information. To this end, a photo coupler having an insulation function to transfer a feedback current is mainly used. However, since the photo coupler is an optical device, signal transfer characteristics depend on photons, a use period, and a junction temperature, such that a circuit design may be complex and a manufacturing cost may be increased, due to the use of the photo coupler.
In order to solve these problems, the power switching control circuit and the driving circuit may be formed on the secondary side. However, in the case of using a scheme of receiving fed-back information regarding a power state on the secondary side to control the switching on the secondary side, it may be difficult to precisely control a switching frequency. Further, in this configuration, since a non-linear device such as a transistor for receiving and directly using the fed-back information on the power state on the secondary side should be additionally used, a manufacturing cost may be further increased.